i) Births and Deaths
NB: I include producers, writers, directors, regular cast and actors who have appeared in more than one story here.
1 July 1934: birth of Jean Marsh, who played the great Sara Kingdom in The Daleks' Master Plan (1965-6). She also appeared as Princess Joanna in The Crusade (1965) and as Morgaine in Battlefield (1989). She has done ten audios for Big Finish, nine as Sara Kingdom. (She was also married to Jon Pertwee, before either was on Doctor Who.)
Also born on 1 July: Daphne Dare (1929), costumer for much of the black and white era; Sonny Caldinez (1932), four-time Ice Warrior who appeared as Kemal the Turk in earlier episodes of Evil of the Daleks; Matthew Jacobs (1956), writer and co-producer of The Movie (1996).
ii) broadcast anniversaries
NB I concentrate on TV releases here, with occasional exceptions.
1 July 1967: broadcast of the seventh and final episode of Evil of the Daleks, Skaro collapsing in flames as the malignant pepperpots battle each other in civil war, and the Second Doctor, Jamie and new companion Victoria flee the ruins as Season Four comes to an end. Sadly, one of the lost episodes.
1 July 2006: broadcast of Army of Ghosts, which starts with that creepy voiceover by Billie Piper about how she died, and then goes on to feature celebrity cameos and Jackie's great line "If we end up on Mars, I'm gonna kill you." Then we get into serious business with Torchwood and the Cybermen, and finally, in the best reveal in the whole of New Who, the Daleks emerge. from the Genesis Ark.
Also 1 July 2006: release of Tardisode 13, a prequel for next week's TV episode, Doomsday.
1 July 2009: broadcast of Torchwood: Asylum, the first of the three radio plays leading up to Children of Earth; this is the one with the strange girl from the future and lots of PC Andy.
1 July 2017: broadcast of The Doctor Falls, last of the tenth season of New Who and the last with Bill and Nardole (and probably with the Gomez and Simm Masters). Poor Bill gets transformed into a Cyberman; the Masters fight each other to the death; and the Doctor starts to regenerate, only to be confronted by a very familiar face at the end.
iii) dates specified in-universe
(Mostly in broadcast stories, with some exceptions as in the first case below)
1 Juy 1997: last day of setting of the 2003 Big Finish audio Sympathy for the Devil, starring David Warner as an alternate-history Doctor, Nicholas Courtney as Brigadier Lethbridge Stewart, and someone called David Tennant as Colonel Brimmicombe-Wood; I wonder what happened to him?
1 July 2058: Date of establishment of Bowie Base One on Mars, as seen in The Waters of Mars (2009).
Plenty more to come.